Which of the following is the substrate for salivary amylase?

• A. Starch
• B. Maltose
• C. Glucose
• D. Sucrose

Answer: (A)

Salivary amylase is the enzyme in saliva that begins carbohydrate digestion in the mouth by breaking the bonds found in starch. Its job is to hydrolyze the internal α-1,4 glycosidic bonds in starch, producing shorter carbohydrates such as maltose and dextrins. The molecule it acts on—the substrate—is starch, a large plant polysaccharide. Maltose, glucose, and sucrose are not substrates for this enzyme; maltose is a product of the reaction, glucose is a later product of further breakdown, and sucrose is acted on by a different enzyme (sucrase) later in the digestive tract. So starch is the correct substrate.